Thermoresponsive fuse



Oct. 6, 1931. N. s NELSON THERMORESPONSIVE FUSE Original Filed Nov. 22,1926 1 vwento'v flf/s 151 1492 $072 roman Patented Oct. 6, 1931 UNITEDSTATES PATENT OFFICE NELS S. NELSON, OF DETROIT, MICHIGAN, ASSIGNOR OFONE-HALF T0 FREDERICK G. MEYER, OF DETROIT, MICHIGAN THERMORESPONSIVEFUSE Substitute for application filed November 22, 1926, Serial No.149,949. This application filed March 5, 1929. Serial No. 344,576.

This invention relates to fuses for the protection of electricalcircuits and appliances, and is. a substitute for application SerialNumber 149,949 filed November 22, 1926, by this applicant.

In the present state of the electrical art, the fuses employed for theabove purpose are of a type comprising a short length of a conductorhaving a thickness adapting it to carry a certain amperage withoutappreciably heating, and formed of a metal that Wlll readily fuseresponsive to the heat generated by an excessive amperage. The breakingof a circuit by such a fuse leaves such circuit permanently dead ordeenergized until a new fuse has been installed. Under such conditions,it is frequently necessary for the current user to remain without lightsor power until the power supply company cansend an employee to install anew fuse. Since the burnt-out fuses are thrown away, the waste whichtheir use involves is a very considerable item, since every electricalinstallation re uires at least one protective fuse.

t is the object of the present invention to provide an improved type offuse, in which the conductor predetermlning the permissible maximiumcurrent It is here lmportant to note that any come mercially practicablesubstitution of thermoflexible elements for the soft metal conductorsnow generally employed a 1n fuses, necessiflow is adopted toautomatically respondto the heat generated by excess temperatures byflexing to a c1r-.

tates employing an extraordinary type of bimetallic conductor, capableof withstanding without detriment at least a red heat, since such a heatwill often be generated in such a conductor before its resultant flexingbreaks the circuit, when the later is shorted or subjected to a suddenheavy overload, The development of such aconductor involves more thanthe mere uniting'of two metals having melting points above thetemperatures arising in use and having the necessary difference in theircoefficients of expansion to cause a flexing response to heat. Theessential characteristic of the metals united to form such a conductoris that they be capable 6 These and various other objects the inven tionattains by the construction hereinafter described and illustrated in theaccompanying drawings, wherein Figure 1 is an axial sectional view of athermal cut-out of the cartridge type, embodying, the resent invention.I

Flgure 2 is a perspective view. of the thermo-responsive element of saidcut-out.

Figure 3 is a cross-sectional 'view taken upon the line 3-3 of Figure 1.

Figure 4 is an axial sectional view ofa screw plug type of the improvedcut-out.

In these views, the reference character 1 designates the usual tubularinsulating casing of a cartridge type of cut-out. Upon the ends of saidcasing there is mounted fast a pair of metal collars 2 and 3 which mayserve to mount the cut-out and to connect it to an electric circuit inthe well known manner. Said collars are held fast upon the casin 1 bythe indenting into the outer surface 0 said collar 2 is further held inplace upon the easing by a contact element 5 which is radially insertedin suitable registering apertures of said collar and easing as is bestseen in Figure 1, said contact preferably projecting some distancewithin the casing.

The outer end of the collar 3 externally threaded for engagement by ascrew cap 6 having a suitably threaded similar flange Get for embracingsaid collar. Between the cap 6 and the collar 3 there is clamped a metaldisk 7 to which is secured one end of the bimetallic theruio-responsivearm 8, 0. The connection between said arm and disk may be established inany suitable manner. as for example, by bending the mounted end portionof the arm against the outer face of the disk and soldering it to saidface. The other or free end of the arm 8, 9 carries a metal contactmember 10 adapted to normally seat against the contact 5. as shown infull lines in Figure 1. The collar 3 is interiorly flanged, as indicatedat 11 to provide an adequate seat for the disk 7 and preferably saidflange has a channel 12 extending from side to side thereof to receivethe arm 8, 9 and thus assist in establishing said arm in its properposition for engagement of the contacts. In assembling the construction.the disk 7 is seated against the flange 11 with the arm 8. 9 projectinginto the casing'l, and engaging in the channel 12. The cap 0 is thenthreaded upon the collar 3, holding said disk and arm securely in place.

A most essential feature-of the described construction is the use ofsuch metals to form the arm 8, 9 as will not suffer a loss ofthermorcsponsiveness under high temperature conditions. It will, ofcourse, be understood that the two rigidly connected strips whichcomprise said arm differ as regards their co-eflicients of expansion.Preferably the arm 8 which has the higher coefficient will be of thefollowing composition z+ Per cent Iron -4. 63.42

Nickel 24.05 Chromium.- 8.14 Silicon 1.88 Manganese .65

Carbon by combination) y .46 Insoluble residue The other arm 9preferably has a composition as follows so formed differ considerably asto their coefficients of expansion and arehencehigh ly responsive totemperature changes. The most important reason, howeveigfor employingalloys of the compositions specified lies in the capacity of said alloysto undergo exceedingly high temperatures (as high at 1500 degrees Fahrenheit)- without detrimentally affecting the power of recovery of thebimetallic element formed by said alloys.

A further highly important feature of the invention lies in the use of anon-welding metal to form the contacts 5 and 10. One example of such ametal is tungsten. The use of such a metal is essential for the reasonthat in use the arm 8, 9 is often subjected to sudden temperature risessuch as tend to fuse the engaging points of said contacts, and suchfusion would be likely to result in a partial welding together of thetwo contacts if the metals were of a nature to permit such an action.

In embodying the invention in a plug type of cut-out such as isillustrated in Figure 4, there is employed the usual hollow insulatingbody 13 open at one end and carrying a terminal button 14 at its closedend, and embraced by a second sleeve-forming terminal member 15 formedwith screw threads. lVithin the chamber 16 of the body 13, near themouth of said chamber there is mounted a contact 17 which is connectedas indicated at 17a to the sleeve terminal 15. Upon the terminal 14there is mounted one end of a bimetallic thermo-responsive arm 18, 19,which carries upon its other or free end a contact 20 coacting with thecontact 17. The metals forming the arm 18, 19 are of the specified heatresistant composition and the contacts 100 17 and 20 are formed oftungsten or some like non-welding metal.

In either of its described and illustrated forms, the invention securesthe desired advantages, and eliminates the loss of time and 105 materialinvolved by the burning out and replacement of fuses.

What I claim is:

1. A thermo-flexible bimetallic circuit breaker arm, retaining its powerof recovery 110 from flexure at temperatures in excess of 1500 degreesFahrenheit, said arm comprising two rigidly connected metal stripsdiffering as to their coefiicients of expansion, the strip of lesserexpansion coefficient contain- 115 ing a predominance of iron, more thanthirty per cent of nickel, less than ten per cent of silicon, and lessthan one per cent each of manganese and carbon.

2. A circuit breaker arm comprising two 1 rigidly connected metalstrips, differing as to their coeflicients of expansion and consequentlythermo-fiexible and maintaining their power of recovery at temperaturesas high as 1500 degrees Fahrenheit, each of said strips 125 containing apredominance of iron, and the strip of lower expansion coefficientcontaining less than twenty-five per cent of nickel, a. lesser quantityof chromium, and still lesser quantities of manganese and carbon, andthe 130 strip of lower expansion coefiicient containing more than thirtyper cent of nickel, less than ten per cent of silicon, and less than oneper cent each of man anese and carbon.

3. A 'thermo-flexi le bimetallic circuit breaker arm, one of the metalsthereof having a higher coeflicient of expansion than the other andbeing of approximately the following composition:

Per cent Iron 63. 42 Nickel 24. 05 Chromium 8. 14 Silicon 1. 88

15 Manganese 65 Carbon 46 Insoluble residue 1. 40

4. A thermo-fiexible, bimetallic circuit breaker arm, one of the metalsthereof having a lower coeflicient of expansion than the other and beingof approximately the following composition Per cent Iron 61. 95

Nickel 37.12

Silicon O7 Manganese 67 Carbon" 19 Intestimony whereof I sign thisspe'cifica tion.

NELS S. NELSON.

